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Vacuum Heat Treatment Furnace

Vacuum Sintering Furnace

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Effect of Vacuum Annealing on Alloy Sheet

TC4 titanium alloy contains 6% α stable element Al and 4% β stable element V, which belongs to the typical α+β type titanium alloy of Ti-Al-V system. This alloy accounts for about 40% of the market volume of titanium alloy series, and it is very difficult to cold work, mainly because the alloy has poor plasticity and high yield ratio, and its mechanical properties and serviceability depend to a large extent on the microstructure. The microstructure mainly depends on the vacuum heat treatment process, so studying the influence of different vacuum annealing processes on properties will play a decisive role in subsequent processing. In addition, it is also necessary to study the dehydrogenation effect of different vacuum annealing to reduce the hydrogen content of the titanium alloy surface layer to a safe concentration, eliminate the possibility of hydrogen embrittlement, and avoid processing cracks.

Melting sponge titanium, high-purity aluminum (99.99%) and aluminum-vanadium alloy in a certain proportion in a vacuum consumable furnace. After forging and rolling, it is made into a semi-finished plate with a thickness of 3.7mm.

The heating temperature in thermal processing is 980℃～1020℃. It was observed that the original β grain boundary in the microstructure obtained by thermal deformation with a deformation rate of 95% was very obvious, the α phase at the grain boundary was very obvious, and the α phase in the grain was arranged in a thick needle shape and regularly. The main reason for this structure is that the heating or deformation of the original blank is carried out in the β phase region, or the original blank is carried out in the β phase region, and when the deformation is performed in the α+β phase region, the amount of deformation taken is small. Grain boundary α is left over from the α phase on the grain boundary without recrystallization due to insufficient deformation. This structure has poor plasticity and high strength. It must undergo intermediate recrystallization annealing to improve its plasticity and reduce strength, creating good deformation conditions for cold working . Observation also found that the grains in the fully deformed zone were fine and obviously elongated.

Anneal the original 3.7mm sample in a vacuum annealing furnace, select the sample plate with the worst plasticity, and take 4 samples. The annealing regimes are 780°C±2°C, 800°C±2°C, 820°C±2°C, 830°C±2°C, vacuum degree ≤0.02Pa, heat preservation for 2 hours, and release at 200°C. After being released from the furnace, the tensile properties and hydrogen content at room temperature were measured. The results showed that:

(1) The vacuum annealing system is 800°C±2°C, holding for 2 hours, which can achieve lower yield strength and the highest plasticity.

(2) The vacuum annealing system is 800°C±2°C, and the temperature is kept for 2 hours, and a stable α+β phase network structure can be obtained.

(3) According to the vacuum degree of the existing vacuum furnace ≤0.02Pa, adopt 800°C±2°C, heat preservation for 2 hours, the hydrogen content is reduced by 0.009% on average compared with the original sample, the dehydrogenation effect is obvious, and no hydrogen will be produced after subsequent cold processing Safe level of brittle (chronic fracture).